A recirculating delay line artefact was used to calibrate the distance scale of an optical time-domain reflectometer (OTDR). The OTDR employed in the measurements was an Anritsu MW9070B equipped with the MW0972B optical unit. The wavelength was set at 1310 nm and the OTDR was operating in fully automatic mode. A group index of 1.467 was assumed. Calibrations and measurements were carried out in accordance with IEC 61 746 document. Overall, results show that the instrument effectively performed distance scale evaluation.